E-mail them. I've been e-mailed by an app developer in a similar situation. I used the app and he was not sure he could keep supporting it and wanted to know if

E-mail them. I've been e-mailed by an app developer in a similar situation. I used the app and he was not sure he could keep supporting it and wanted to know if his users would be willing to pay him. It was not an issue for me as it was a legitimate, app-related communication.